Within hours of the fall of Fort Sumter, on April 14, 1861, damage from the Confederate bombardment of it that started the Civil War had been photographed.

This was something new — the first time Americans would see images of war, as it really looked . . . the first time true likenesses of the people who lived and died in the conflict remained as a record, profoundly shaping our understanding of the bloodiest war in U.S. history.

“When the Civil War began, photography was really in its infancy, it was just 20 years old,” said Jeff Rosenheim, who heads the photography department at the Metropolitan Museum of Art in New York.

He is also curator of the exhibition, “Photography and the American Civil War.”

He showed Teichner examples of portraits taken of Civil War soldiers.

“They were kept in little pocket albums, little leather albums, both by regular soldiers and by officers,” said Rosenheim. “They were kept on the person, next to your heart.”

Such as the portrait found in the hands of a dead soldier after the Battle of Gettysburg.

In these portraits, you see how young the soldiers were — often, just boys — or how ferocious they tried to look, such as the portrait of the four Pattillo Brothers, each holding a giant blade.

From left: Benjamin, George, James and John Pattillo, of Henry County, Ga., are pictured holding a Bowie or side knife. They has joined Company K of the 22nd Regiment of the Georgia Volunteer Infantry. / David Wynn Vaughn Collection

Photographs were already cheap — 50 to 75 cents, with a fancy folding case, or five to ten cents printed like glorified postcards.

Subjects had to sit or stand absolutely still for as long as eight seconds then. Pictures were taken on glass plates, and printed outside in the sun.

There were field studios in tents with skylights. Very early on, photo supplies became almost impossible to get in the South, so photographers followed the Union armies, and edged closer and closer to the battlefield.

Photojournalism was born during the Civil War, though with limitations: You could take pictures before the battle, and after the battle, but not during the battle, because of the long exposures required. “The camera really couldn’t capture that movement,” said Rosenheim.

Alexander Gardner’s camera captured the dead of Antietam, after the bloodiest battle of our bloodiest war, on Sept. 17, 1862. In fact, our bloodiest day ever, with 23,000 dead and wounded.

“A Burial Party, Cold Harbor, Virginia,” photographed by John Reekie in 1865, depicts African American soldiers collecting corpses from the site of a massive battle which took place in May-June 1864.

And then came Gettysburg the following summer — 150 years ago this month.

The beauty of the place belies the awfulness in Gardner’s photographs, shocking to this day. You can still match locations now with then, which adds to the intrigue of a famous photographic controversy.

Rosenheim showed Teichner two images of a fallen Confederate soldier: One titled “Home of a Rebel Sharpshooter,” and another, “Sharpshooter’s Last Sleep.”

It’s the same sharpshooter in both pictures.

How did that happen? “Some suggest that the photographer, Gardner, and his assistant, Timothy O’Sullivan, found it in the open field and moved it to this little nesty area,” said Rosenheim. “Other people believe that the body was found here and removed by a burial detail to this [other] location.”

Pictures of the wounded were equally gruesome. A Washington surgeon used them to teach medical students.

There were also photographs taken of emancipated slaves; the little four-inch pictures were sold to raise money for the education of former slaves in Louisiana. But abolitionists quickly figured out they were a powerful argument for the anti-slavery cause — as in the images of slave children who look white, or the 1863 photo of an emancipated slave whose forehead bore the scars of a brand, the initials of the Louisiana plantation owner who once owned him.

One photo, title “The Scourged Back,” found its way into the film, “Lincoln.”

Abraham Lincoln understood the importance of photography even before the Civil War. A photo taken in 1860 by Mathew Brady, America’s most famous photographer at the time, was reproduced in many forms, including campaign buttons. It was widely believed to have gotten candidate Lincoln elected president.

He was photographed often during his presidency — the change in him, as the war took its toll, very plain. And when he was assassinated in April 1865, photography was part of the manhunt, with the first wanted poster in American history illustrated with photographs.

“Photography was everywhere,” said Rosenheim. “It had really saturated American society, and they just needed to actually go to the boarding house, to the family homes, to the friends of the likely conspirators to find pictures of them.”

John Wilkes Booth was killed. Four were hanged. Pictures taken at the gallows were printed and sold. People collected them, recognizing that the story they told was important.

“I think that we are, as a nation, only as good as our memory,” said Rosenheim, “and the facts of these photographs, their tradition, gives us something that we cannot forget.

What we really have is the beginning of an archive — an archive of who we are, or at least who we were,” said Rosenheim. “That is the treasury that we build our history from.”

-CBSNews.com